Catalyst systems

ABSTRACT

Catalyst systems suitable for tetramerizing ethylene to form 1-octene may include a catalyst comprising a chromium compound coordinated with a ligand and a co-catalyst comprising an organoaluminum compound. The ligand may include have a chemical structure according to formula (I), wherein at least one of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 , R 11 , and R 12  have the structure according to formula (II) wherein R A , R B , R C , and R D  and the remainder of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 , R 11 , and R 12  are independently chosen from a hydrogen or a (C 1 -C 50 ) hydrocarbyl group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Application Ser. No. 63/237,377 filed on Aug. 26, 2021, and entitled “Catalyst Systems,” the entire contents of which are incorporated by reference in the present disclosure.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to chemical processing and, more particularly, catalyst systems utilized in such chemical processing.

BACKGROUND

Linear alpha-olefins (“LAOs”) are typically produced via the cracking of refinery products or the non-selective oligomerization of ethylene, which results in a broad alpha-olefin distribution. Currently, there are several industrial processes that produce LAOS, such as the Shell Higher Olefin Process (SHOP), which has been in operation since 1977. SHOP employs a combination of oligomerization and olefin metathesis chemistries to produce a variety of LAOs using a nickel-based catalyst. INEOS, a global manufacturer of petrochemicals, has also developed a proprietary process for synthesizing a wide range of LAOs with the flexibility to change distributions of products to meet demand.

However, demand for LAOs is rising in North America, Western Europe, and Asia. In particular, demand for short chain alpha olefins, such as 1-octene and 1-hexene, is rising due to their significance to a number of specific applications. For example, 1-octene may be used to improve the rheological melt and solid resin properties of polyethylene. As a result, the main consumer of 1-octene is the industry responsible for the high-volume production of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), which expands each year. The content of 1-octene may be from 1% to 2% in HDPE, and as much as 10% in some LLDPE grades.

Based on this, 1-octene is a significant chemical feedstock that is in market demand. Aside from the processes discussed above, various catalysts have been developed for the tetramerization of ethylene to selectively form 1-octene. However, these catalysts have deficiencies in several respects. Accordingly, improved catalysts, which are suitable for tetramerization of ethylene to selectively form 1-octene, are desired in the industry.

SUMMARY

Fouling, as described in the present disclosure, refers to the undesirable formation of polymers. Such polymers may form as side-products in the reaction of ethylene to form 1-octene when a catalyst system including chromium is used. However, as described in the present disclosure, it has been discovered that the utilization of a particular ligand that comprises a PNP moiety and a triptycene moiety as described herein, which may coordinate with chromium, may reduce fouling. Moreover, in some embodiments, the utilization of catalysts including the ligands may contribute to maintaining the selectivity of 1-octene, or even enhancing the selectivity of 1-octene, as compared with similar catalyst systems that do not include the ligand.

According to one or more embodiments, a catalyst system suitable for tetramerizing ethylene to form 1-octene may include a catalyst comprising a chromium compound coordinated with a ligand and a co-catalyst comprising an organoaluminum compound. The ligand may have a chemical structure according to formula (I).

In formula (I), at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ have the structure according to formula (II).

In formula (II), R_(A), R_(B), R_(C), and R_(D) and the remainder of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.

Additional features and advantages of the aspects of the present disclosure will be set forth in the detailed description that follows and, in part, will be readily apparent to a person of ordinary skill in the art from the detailed description or recognized by practicing the aspects of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a reaction scheme for forming a ditopic ligand according to the embodiment of Example 1.

DETAILED DESCRIPTION

The present disclosure describes catalyst systems that may be utilized to produce 1-octene from ethylene by tetramerization. Also described are methods for utilizing such catalyst systems. The presently described catalyst systems may include a catalyst and a co-catalyst, which are described in detail. In one or more embodiments, the catalyst may include chromium and a ligand. The co-catalyst may include an organoaluminum compound. In one or more embodiments, the ligand may include a PNP moiety and a triptycene moiety.

In one or more embodiments, the catalyst systems described in the present disclosure may be used to selectively tetramerize ethylene to produce 1-octene, while reducing undesirable polymerization, sometimes referred to as “fouling” as compared to other known catalysts. Fouling may occur at least partially due to the formation of solid polyethylene-based residues, which may reduce fluid flow and/or fully block or at least partially block fluids in a reactor system from flowing at a desired rate. Without being bound by any particular theory, it is believed that the incorporation of the ligand described in the present disclosure into the catalyst system reduces fouling while maintaining a suitable yield of 1-octene.

It should be understood that the catalyst systems described in the present disclosure may not completely eliminate fouling during a reaction. However, in one or more embodiments, these catalyst systems reduce fouling as compared with catalyst systems that do not include a ligand as described in the present disclosure. Additionally, it should be understood that while these catalyst systems may be useful for the catalysis of the oligomerization of ethylene, such as the tetramerization of ethylene to form 1-octene, they may also be useful for the catalysis of other chemical reactions. As a result, these catalyst systems should not be considered limited in their use to the tetramerization of ethylene to form 1-octene.

As used in the present disclosure, the term “catalyst” refers to any substance that increases the rate of a specific chemical reaction. Catalysts described in this disclosure may be utilized to promote various reactions, such as, but not limited to, the tetramerization of ethylene to form 1-octene. Catalysts are generally not consumed in a reaction, but as would be understood in the art, may have reduced catalytic activity over time and need to be replaced and/or regenerated.

As used in the present disclosure, the term “co-catalyst” (also referred to as an activator and/or scavenger) generally refers to any substance or chemical agent that brings about catalysis of a chemical reaction in conjunction with one or more catalysts. In some embodiments, a catalyst may have independent catalytic functionality, while in other embodiments the catalyst may only have substantial catalytic functionality when paired with a co-catalyst. It should be understood that the catalyst and co-catalyst may be, in some embodiments, bonded or formed in a complex, but in other embodiments are not bonded or present in a complex. Some co-catalysts may be said to “activate” a catalyst, which may increase catalytic functionality.

As used in the present disclosure, the term “catalyst system” refers to any catalytically functional collection of chemical species. In one or more embodiments, a catalyst system may include a catalyst and a co-catalyst. In some embodiments, a catalyst system may include additional components, such as, for example, additional co-catalysts or non-catalytic additives which may serve other purposes.

As used in the present disclosure, the term “independently chosen” means that the R groups, such as, R₁, R₂, and R₃, can be identical or different. For example, R₁, R₂, and R₃ may all be substituted alkyls; or R₁ and R₂ may be a substituted alkyl, and R₃ may be an aryl. A chemical name associated with an R group is intended to convey the chemical structure that is recognized in the art as corresponding to that of the chemical name. As a result, chemical names are intended to supplement and illustrate, not preclude, the structural definitions known to those of skill in the art.

As used in the present disclosure, the term “reaction product” refers to a chemical species formed from the reaction of any two or more reactant species or reagents. A reaction product may result in a covalent or ionic bond, coordination, or other interaction between reactant species. In one or more embodiments, two or more reaction products may result from the reaction of the reactant species, and all of these possible produced chemical species are included in the reaction product.

When used to describe certain carbon atom-containing chemical groups, a parenthetical expression having the form “(C_(x)-C_(y))” means that the unsubstituted form of the chemical group has from x carbon atoms to y carbon atoms, inclusive of x and y. For example, a (C₁-C₅₀) alkyl group is an alkyl group having from 1 to 50 carbon atoms in its unsubstituted form. In some embodiments and general structures, certain chemical groups may be substituted by one or more substituents. A substituted chemical group defined using the “(C_(x)-C_(y))” parenthetical may contain more than y carbon atoms depending on the identity of any substituents. For example, a “(C₁-C₅₀) alkyl substituted with exactly one phenyl (—C₆H₅)” may contain from 7 to 56 carbon atoms. Thus, in general when a chemical group defined using the “(C_(x)-C_(y))” parenthetical is substituted by one or more carbon atom-containing substituents, the minimum and maximum total number of carbon atoms of the chemical group is determined by adding to both x and y the combined sum of the number of carbon atoms from all of the carbon atom-containing substituents.

The term “substitution” means that at least one hydrogen atom (—H) bonded to a carbon atom or heteroatom of a corresponding unsubstituted compound or functional group is replaced by a substituent. Substituents may be any suitable functional group or radical that could replace a hydrogen atom bonded to a carbon atom or heteroatom of a corresponding unsubstituted compound. For example, substituents may include, but are not limited to, hydrocarbyls, cyclohydrocarbyls, aryls, halogens, and amines.

The term “—H” means a hydrogen or hydrogen radical that is covalently bonded to another atom. “Hydrogen” and “—H” are interchangeable, and unless clearly specified have identical meanings.

The term “hydrocarbyl” means a monovalent radical resulting from removal of any hydrogen atom from a hydrocarbon, including aromatic hydrocarbons, non-aromatic hydrocarbons, cyclic or acyclic hydrocarbons, saturated or unsaturated hydrocarbons, straight chain or branched chain hydrocarbons, and substituted or unsubstituted hydrocarbons.

The term “heterohydrocarbyl” refers to a hydrocarbyl, from which at least one carbon atom has been replaced with a heteroatom. Examples of heteroatoms include, without limitation, oxygen, nitrogen, sulfur, and phosphorus.

The term “cyclohydrocarbyl” means an aromatic or non-aromatic, cyclic hydrocarbyl having at least three carbon atoms, including monocyclic and polycyclic hydrocarbyls, fused and non-fused polycyclic hydrocarbyls, and bicyclic hydrocarbyls, non-aromatic saturated or unsaturated cyclic hydrocarbyls, and substituted or unsubstituted hydrocarbyls.

The term “aryl” means an aromatic hydrocarbon radical, in which the carbon atoms of the aromatic system may be substituted or unsubstituted. Aryls include monocyclic, bicyclic and tricyclic aromatic hydrocarbon radicals. A monocyclic aromatic hydrocarbon radical includes one aromatic ring; a bicyclic aromatic hydrocarbon radical has two rings; and a tricyclic aromatic hydrocarbon radical has three rings. When the bicyclic or tricyclic aromatic hydrocarbon radical is present, at least one of the rings of the radical is aromatic. The other ring or rings of the aromatic radical may be independently fused or non-fused and aromatic or non-aromatic. Non-limiting examples of aryls include phenyl; fluorenyl; tetrahydrofluorenyl; indacenyl; hexahydroindacenyl; indenyl; dihydroindenyl; naphthyl; tetrahydronaphthyl; and phenanthrenyl.

The term “alkyl” means a saturated hydrocarbon radical that may be linear or branched. Accordingly, the term “(C₁-C₂₀) alkyl” means a saturated linear or branched hydrocarbon radical of from 1 to 20 carbon atoms that is unsubstituted or substituted. Examples of unsubstituted (C₁-C₂₀) alkyl include methyl; ethyl; 1-propyl; 2-propyl; 1-butyl; 2-butyl; 2-methylpropyl; 1,1-dimethylethyl; 1-pentyl; 1-hexyl; 1-heptyl; 1-nonyl; and 1-decyl. Examples of substituted (C₁-C₂₀) alkyl include trifluoromethyl and trifluoroethyl.

The term “saturated” means lacking carbon-carbon double bonds, carbon-carbon triple bonds, and (in heteroatom-containing groups) carbon-nitrogen, carbon-phosphorous, and carbon-silicon double bonds. Where a saturated chemical group is substituted by one or more substituents, one or more double and/or triple bonds optionally may be present in substituents. The term “unsaturated” means containing one or more carbon-carbon double bonds or carbon-carbon triple bonds, or (in heteroatom-containing groups) one or more carbon-nitrogen double bonds, carbon-phosphorous double bonds, or carbon-silicon double bonds, not including double bonds that may be present in substituents, if any, or in aromatic rings or heteroaromatic rings, if any.

As noted previously, the embodiments of the present disclosure are directed to a catalyst system suitable for tetramerizing ethylene to form 1-octene. In one or more embodiments, the catalyst system includes a catalyst. In some embodiments, the catalyst includes chromium. It should be understood that, as contemplated in the present disclosure, a catalyst that includes chromium may be any chemical compound that includes chromium and is catalytically functional for, without limitation, promoting the tetramerization of ethylene to from 1-octene.

In one or more embodiments, the catalyst includes a chromium compound and a ligand. It should be understood that the chromium complexes described herein, which may coordinate with one or more ligands, are not necessarily limited in structure, but include chromium. In some embodiments, the chromium compound includes an organic chromium salt, an inorganic chromium salt, a chromium coordination, a chromium organometallic complex, or combinations of these. In some embodiments, the chromium compound includes a chromium trichloride tris-tetrahydrofuran complex, (benzene)tricarbonyl chromium, chromium (III) octanoate, chromium (III) acetylacetonoate, chromium hexacarbonyl, chromium (III) 2-ethylhexanoate, [CrCl₂(μ-Cl)(THF)₂]₂, CrCl₂(THF)₂, Chromium(III) pyridine-2-carboxylate, Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)chromium(III), or combinations of these.

The chromium compound may be produced using procedures and methods known in the art. For example, procedures and methods for producing the chromium compound are described in U.S. Pat. No. 7,297,832, which is incorporated by reference in its entirety.

It should be understood that the ligands described herein, which may coordinate with the chromium atom of the chromium compound are not necessarily limited in structure. However, in one or more embodiments, the ligand may have a structure according to formula (I):

In formula (I) at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ may have a structure according to formula (II):

In formulas (I) and (II), the remainder of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ and R_(A), R_(B), R_(C), and R_(D) may be independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group. In embodiments, the (C₁-C₅₀) hydrocarbyl group may be a substituted or unsubstituted (C₁-C₅₀) linear or branched hydrocarbyl group, a substituted or unsubstituted (C₃-C₅₀) cyclohydrocarbyl group, or a substituted or unsubstituted (C₄-C₅₀) aryl group. In some embodiments the (C₁-C₅₀) hydrocarbyl group may be a (C₁-C₅₀) heterohydrocarbyl group. In one or more embodiments, the remainder of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ and R_(A), R_(B), R_(C), and R_(D) may be independently chosen from hydrogen, a substituted or unsubstituted (C₁-C₅₀) linear or branched alkyl group, a substituted or unsubstituted (C₃-C₅₀) cyclohydrocarbyl group, or a substituted or unsubstituted (C₆-C₅₀) aryl group. In some embodiments, each of R_(A), R_(B), R_(C), and R_(D) may be an unsubstituted (C₆-C₅₀) aryl group.

Still referring to formula (I), in some embodiments, R₃ may have the structure of formula (II). In some embodiments, R₁ and R₄ may have the structure of formula (II). In such embodiments, the remainder of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ and R_(A), R_(B), R_(C), and R_(D) are as described hereinabove with respect to formulas (I) and (II).

In one or more embodiments, the ligand may have a structure according to formula (III):

In formula (III), R_(A), R_(B), R_(C), R_(D), R₁, R₇, and R₁₀ may be independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group. In embodiments, the (C₁-C₅₀) hydrocarbyl group may be a substituted or unsubstituted (C₁-C₅₀) linear or branched hydrocarbyl group, a substituted or unsubstituted (C₃-C₅₀) cyclohydrocarbyl group, or a substituted or unsubstituted (C₄-C₅₀) aryl group. In some embodiments the (C₁-C₅₀) hydrocarbyl group may be a (C₁-C₅₀) heterohydrocarbyl group, a (C₃-C₅₀) heterocyclohydrocarbyl group, or a (C₄-C₅₀) heteroaryl group. In some embodiments, each of R_(A), R_(B), R_(C), R_(D), R₁, R₇, and R₁₀ may be independently chosen from hydrogen, a substituted or unsubstituted (C₁-C₅₀) linear or branched alkyl group, a substituted or unsubstituted (C₃-C₅₀) cyclohydrocarbyl group, or a substituted or unsubstituted (C₆-C₅₀) aryl group. In one or more embodiments, each of R_(A), R_(B), R_(C), and R_(D) may be an unsubstituted (C₆-C₅₀) aryl group. In some embodiments, each of R₁, R₇, and R₁₀ are hydrogen.

In some embodiments, R_(A), R_(B), R_(C), and R_(D) of formula (III) may be independently chosen from a benzyl, phenyl, tolyl, xylyl, mesityl, biphenyl, naphthyl, anthracenyl, methoxy, ethoxy, and other alkoxy, phenoxy, tolyloxy, and other aryloxy, dimethylamino, diethylamino, methylethylamino, thiophenyl, pyridyl, thioethyl, thiophenoxy, trimethylsilyl, dimethylhydrazyl, methyl, ethyl, and other alkyl, ethenyl, propenyl, and other alkenyl, propyl, butyl, and other alkyl, propynyl, and other alkynyl, cyclopentyl, cyclohexyl, and other cycloalkyl, ferrocenyl, or tetrahydrofuranyl group.

In some embodiments, R_(A) and R_(B) or R_(C) and R_(D) may be bonded such that a cyclic moiety including P is formed. For example, R_(A) and R_(B) may be bonded such that a cyclic moiety including P is formed. Likewise, R_(C) and R_(D) may be bonded such that a cyclic moiety including P is formed. In one or more embodiments, R_(A), R_(B), and P may form a phospholane group. In one or more embodiments, R_(C), R_(D), and P may form a phospholnae group. As described herein, a “phospholane group” refers to a cyclic organophosphorous compound comprising a five membered ring including phosphorous and four carbon atoms. In some embodiments, the phospholane compound may be unsubstituted or may be substituted by one or more hydrocarbyl groups. Cyclic moieties that may be formed from R_(A), R_(B), and P or R_(C), R_(D), and P in some embodiments are depicted in formulas (IV) to (XI).

In one or more embodiments, the ligand may have a structure according to formula (XII):

In formula (XII), R_(A), R_(B), R_(C), R_(D), R₃, R₇, and R₁₀ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group. In embodiments, the (C₁-C₅₀) hydrocarbyl group may be a substituted or unsubstituted (C₁-C₅₀) linear or branched hydrocarbyl group, a substituted or unsubstituted (C₃-C₅₀) cyclohydrocarbyl group, or a substituted or unsubstituted (C₄-C₅₀) aryl group. In some embodiments the (C₁-C₅₀) hydrocarbyl group may be a (C₁-C₅₀) heterohydrocarbyl group, a (C₃-C₅₀) heterocyclohydrocarbyl group, or a (C₄-C₅₀) heteroaryl group. In some embodiments, each of R_(A), R_(B), R_(C), R_(D), R₃, R₇, and R₁₀ may be independently chosen from hydrogen, a substituted or unsubstituted (C₁-C₅₀) linear or branched alkyl group, a substituted or unsubstituted (C₃-C₅₀) cyclohydrocarbyl group, or a substituted or unsubstituted (C₆-C₅₀) aryl group. In one or more embodiments, each of R_(A), R_(B), R_(C), and R_(D) may be an unsubstituted (C₆-C₅₀) aryl group. In some embodiments, each of R₃, R₇, and R₁₀ are hydrogen.

In some embodiments, R_(A), R_(B), R_(C), and R_(D) of formula (XII) may be independently chosen from a a benzyl, phenyl, tolyl, xylyl, mesityl, biphenyl, naphthyl, anthracenyl, methoxy, ethoxy, and other alkoxy, phenoxy, tolyloxy, and other aryloxy, dimethylamino, diethylamino, methylethylamino, thiophenyl, pyridyl, thioethyl, thiophenoxy, trimethylsilyl, dimethylhydrazyl, methyl, ethyl, and other alkyl, ethenyl, propenyl, and other alkenyl, propyl, butyl, and other alkyl, propynyl, and other alkynyl, cyclopentyl, cyclohexyl, and other cycloalkyl, ferrocenyl, or tetrahydrofuranyl group.

In some embodiments, R_(A) and R_(B) or R_(C) and R_(D) may be bonded such that a cyclic moiety including P is formed. For example, R_(A) and R_(B) may be bonded such that a cyclic moiety including P is formed. Likewise, R_(C) and R_(D) may be bonded such that a cyclic moiety including P is formed. In one or more embodiments, R_(A), R_(B), and P may form a phospholane group. In one or more embodiments, R_(C), R_(D), and P may form a phospholnae group. As described herein, a “phospholane group” refers to a cyclic organophosphorous compound comprising a five membered ring including phosphorous and four carbon atoms. In some embodiments, the phospholane compound may be unsubstituted or may be substituted by one or more hydrocarbyl groups. Cyclic moieties that may be formed from R_(A), R_(B), and P or R_(C), R_(D), and P in some embodiments are depicted in formulas (IV) to (XI), as shown herinabove.

In one or more embodiments, the ligand may be 1,4-triptycene(N(PPh₂)₂)₂.

In one or more embodiments, the catalyst may include the ligand in an amount such that a molar ratio of the ligand to chromium in the catalyst is from 0.1 to 10.0. For example, the molar ratio of the ligand to chromium in the catalyst may be from 0.1 to 9.0, from 0.1 to 8.0, from 0.1 to 7.0, from 0.1 to 6.0, from 0.1 to 5.0, from 0.1 to 4.0, from 0.1 to 3.0, from 0.1 to 2.0, from 0.1 to 1.0, from 1.0 to 10.0, from 1.0 to 9.0, from 1.0 to 8.0, from 1.0 to 7.0, from 1.0 to 6.0, from 1.0 to 5.0, from 1.0 to 4.0, from 1.0 to 3.0, from 1.0 to 2.0, from 2.0 to 10.0, from 2.0 to 9.0, from 2.0 to 8.0, from 2.0 to 7.0, from 2.0 to 6.0, from 2.0 to 5.0, from 2.0 to 4.0, from 2.0 to 3.0, from 3.0 to 10.0, from 3.0 to 9.0, from 3.0 to 8.0, from 3.0 to 7.0, from 3.0 to 6.0, from 3.0 to 5.0, from 3.0 to 4.0, from 4.0 to 10.0, from 4.0 to 9.0, from 4.0 to 8.0, from 4.0 to 7.0, from 4.0 to 6.0, from 4.0 to 5.0, from 5.0 to 10.0, from 5.0 to 9.0, from 5.0 to 8.0, from 5.0 to 7.0, from 5.0 to 6.0, from 6.0 to 10.0, from 6.0 to 9.0, from 6.0 to 8.0, from 6.0 to 7.0, from 7.0 to 10.0, from 7.0 to 9.0, from 7.0 to 8.0, from 8.0 to 10.0, from 8.0 to 9.0, or from 9.0 to 10.0.

In one or more embodiments, the catalyst system also includes a co-catalyst. In some embodiments, the co-catalyst may include an organoaluminum compound. As described in the present disclosure, the term “organoaluminum compound” refers to any chemical compound that includes at least one aluminum atom and any organic moiety. It should be appreciated that the organoaluminum compound may include several chemical species, or may be a single chemical species. In some embodiments, the organoaluminum compound may be an alkyl aluminum compound. The aluminum alkyl compound may, for example, have a structure according to formula (XIII):

In formula (XIII), R₁₃, R₁₄ and R₁₅ are each independently chosen from hydrogen, an unsubstituted (C₁-C₂₀) linear or branched alkyl group, an oxygen-containing moiety, or a halide. In some embodiments, the alkyl aluminum compound may be an aluminoxane structure (a partial hydrolysate of a trialkylaluminum compound). For example, suitable aluminum alkyl compounds may include trimethylaluminium, triethylaluminum, tripropylaluminum, tri-iso-butylaluminum, diisoblitylaluminium hydride. trihexylaluminum, tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, aluminium isopropoxide, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, methylaluminoxane (MAO), ethylaluminoxane (EAO), isobutylaluminoxane (iBAO), and modified alkylaluminoxanes, such as modified methylaluminoxane (MMAO). As described in the present disclsoure, the term “modified alkylaluminoxane” refers to an alkylaluminoxane that includes one or more modifier groups, such as isobutyl or n-octyl groups in addition to the alkyl groups. In one or more embodiments, the organoaluminum compound of the catalyst system may comprise, consist essentially of, or consist of any of these compounds.

In one or more embodiments, the catalyst system may include the co-catalyst in an amount such that a molar ratio of aluminum to chromium in the catalyst system is from 0.1 to 10.0. For example, the molar ratio of aluminum to chromium in the catalyst system may be from 0.1 to 9.0, from 0.1 to 8.0, from 0.1 to 7.0, from 0.1 to 6.0, from 0.1 to 5.0, from 0.1 to 4.0, from 0.1 to 3.0, from 0.1 to 2.0, from 0.1 to 1.0, from 1.0 to 10.0, from 1.0 to 9.0, from 1.0 to 8.0, from 1.0 to 7.0, from 1.0 to 6.0, from 1.0 to 5.0, from 1.0 to 4.0, from 1.0 to 3.0, from 1.0 to 2.0, from 2.0 to 10.0, from 2.0 to 9.0, from 2.0 to 8.0, from 2.0 to 7.0, from 2.0 to 6.0, from 2.0 to 5.0, from 2.0 to 4.0, from 2.0 to 3.0, from 3.0 to 10.0, from 3.0 to 9.0, from 3.0 to 8.0, from 3.0 to 7.0, from 3.0 to 6.0, from 3.0 to 5.0, from 3.0 to 4.0, from 4.0 to 10.0, from 4.0 to 9.0, from 4.0 to 8.0, from 4.0 to 7.0, from 4.0 to 6.0, from 4.0 to 5.0, from 5.0 to 10.0, from 5.0 to 9.0, from 5.0 to 8.0, from 5.0 to 7.0, from 5.0 to 6.0, from 6.0 to 10.0, from 6.0 to 9.0, from 6.0 to 8.0, from 6.0 to 7.0, from 7.0 to 10.0, from 7.0 to 9.0, from 7.0 to 8.0, from 8.0 to 10.0, from 8.0 to 9.0, or from 9.0 to 10.0.

In one or more embodiments, ethylene may be contacted with the catalyst system to from a reaction product including 1-octene. Contacting may generally include any mixing and/or combining of the reactant ethylene with the catalyst system. In some embodiments, the catalyst and co-catalyst may be separately prepared as solutions, and then combined, prior to contacting of the catalyst system with ethylene. In some embodiments, the catalyst system may be contacted with ethylene in the presence of one or more reaction mediums. Suitable reaction mediums may include, for example, cyclohexane (CyH), methylcyclohexane (MeCy), decahydronapthalene (DHN), 2,2,4-trimethylpentane (TMP), and chlorobenzene (PhCl ). In some embodiments, the ethylene may be contacted with the catalyst system in the presence of hydrogen.

In one or more embodiments, the reaction may be performed as a batch reaction or as a continuous process reaction, such as a continuous stir tank reactor process. In some embodiments, the pressure of the reactor may be from 2 bar to 100 bar (such as from 10 bar to 50 bar), and the reactor temperature may be from 30° C. to 120° C. (such as from 30° C. to 75° C.). However, process conditions outside of these ranges are contemplated, especially in view of the specific design of the reactor system and concentrations of the reactants and catalyst system.

It should be understood that, in one or more embodiments, similar catalyst systems that do not include the ligand of the present application may exhibit increased fouling compared to the catalyst system of the present application. In one or more embodiments, the inclusion of the ligand in a catalyst system may suppress polymer formation while not greatly reducing the yield of 1-octene. In one or more embodiments, polymer formation (fouling) may be reduced by at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or even 95% by the inclusion of the ligand. For example, the reaction product of the tetramerization of ethylene using the catalyst system may include less than 15 wt. %, less than 12 wt. %, less than 9 wt. %, less than 6 wt. %, or less than 3 wt. % of polymer.

In one or more embodiments, 1-octene production may be increased, stay the same, or may decrease by less than or equal to 50%, 40%, 30%, 20%, 10% or even 5% by the inclusion of the ligand. For example, the reaction product of the tetramerization of ethylene using the catalyst system may include greater than 50 wt. %, greater than 55 wt. %, greater than 60 wt. %, greater than 65 wt. %, or greater than 70 wt. % of 1-octene.

In one or more embodiments, the catalyst system may both reduce the polymer formation (such as by at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or even 95%) and increase, not effect, or decrease 1-octene production rate by less than or equal to 50%, 40%, 30%, 20%, 10% or even 5%. Reduction in polymer formation rates and catalytic activity on a percentage basis are based on catalyst systems that include the ligand of the present disclosure as compared with catalyst systems that do not include the ligand of the present disclosure.

In one or more embodiments, the catalyst system may have increased activity compared to similar catalyst systems that do not include the ligand of the present disclosure. As used in the present disclosure, the term “activity” refers to the amount of reaction product produced (in kilograms) per the amount of chromium compound used (in grams) per hour (kg·gc_(r) ⁻¹·h⁻¹). In some embodiments, the catalyst system may have an activity greater than 10 kg·gc_(r) ⁻¹·h⁻¹, greater than 100 kg·gc_(r) ⁻¹·h⁻¹, greater than 250 kg·gc_(r) ⁻¹·h⁻¹, greater than 500 kg·gc_(r) ⁻¹·h⁻¹, greater than 750 kg·gc_(r) ⁻¹·h⁻¹, greater than 1,000 kg·gc_(r) ⁻¹·h⁻¹, or greater than 1,150 kg·gc_(r) ⁻¹·h⁻¹.

EXAMPLES

The various aspects of the present disclosure will be further clarified by the following examples. The examples are illustrative in nature and should not be understood to limit the subject matter of the present disclosure.

A diptopic ligand was formed as depicted in FIG. 1.

First, 9.55 g (53.7 mmol) of Anthracene was recrystallized from p-xylene, and quinone (5.80 g, 53.7 mmol) was purified by sublimation at 100° C. Then, the anthracene and quinone were added to 55.0 mL of xylene. The mixture was heated to a temperature of 120° C. and held under reflux for three hours under an Ar atmosphere. A solid was collected on a filter paper and was washed with hot water to remove any quinone and quinhydrone. The remaining solid was further washed with n-hexane and dried under vacuum at 100° C. for 10 hours. The yield was 10.2 g (67%). The formation of Adduct (I) was confirmed by GC-MS analysis (m/z=286.1).

Then, 2.25 g (7.87 mmol) of Adduct (I) was dissolved in 28 mL of glacial acetic acid. The solution was heated to its boiling point and a few drops of 40% hydrobromic acid were added to the solution. A vigorous evolution of heat followed the addition of the hydrobromic acid and the solution took on an orange color. The orange color gradually faded as a fine white solid precipitated out of the solution. The solution was held at its boiling point for 1.5 hours, at which time, the solution was cooled and filtered. The yield of triptycene-1,4-hydroquinone, Adduct (II), was 1.8 g (82%). The formation of triptycene-1,4-hydroquinone was confirmed by GC-MS analysis(m/z=286.3).

Then, 1.4 g (4.9 mmol) of the triptycene-1,4-hydroquinone was dissolved in 110 mL of glacial acetic acid in a one-neck 250 mL round bottom flask equipped with a magnetic stir bar. The solution was brought to its boiling point and 30 mL of a 1.3% (w/v) potassium bromate solution was added. The mixture was refluxed for 5 minutes. Then, 20 mL of hot water was added, and the mixture was refluxed for 5 minutes. The mixture was cooled and an orange solid was filtered from the mixture. The solid was washed with acetic acid, and then the solid was washed with water. The solid, triptycene-1,4-quinone, Adduct (III), was dried at 100° C. The yield of triptycene-1,4-quinone was 1.4 g (80%). The formation of triptycene-1,4-quinone was confirmed by GC-MS analysis (m/z=284.3).

Then, 1.4 g (4.9 mmol) of triptycene-1,4-quinone, 4.0 g of hydroxylamine hydrochloride, and 100 mL of ethanol were added to a 250 mL two-neck flask equipped with a magnetic stir bar and nitrogen protection. The mixture was refluxed overnight and then a solid was precipitated in water. The solid was collected and recrystallized in acetic acid. The crystals of triptycene-1,4-dioxime, Adduct (IV), were dried under vacuum at 100° C. overnight.

Then, 1.12 g (0.035 mol) of triptycene-1,4-dioxime, 0.113 g. of 10% Pd/C catalyst, and 45 mL of ethanol were added to a 250 ML 2-neck round bottom flask equipped with a magnetic stir bar and nitrogen protection. The mixture was brought to reflux at 80° C. and 3.1 g of hydrazine monohydrate was added dropwise. The reaction mixture was allowed to reflux overnight. The catalyst was then removed by vacuum filtration through packed Celite® and the ethanol was removed under vacuum. The 1,4-triptycenediamine was collected and dried under vacuum at 100° C. overnight. The yield of 1,4-triptycenediamine was 0.9 g (89%). The formation of 1,4-triptycenediamine was confirmed by GC-MS analysis (m/z=284.3).

Then, 0.161 g (0.567 mmol) of 1,4-triptycenediamine and 0.34 g (3.4 mmol) of trimethylamine were dissolved in 8 mL of dichloromethane. 0.5 g (2.26 mmol) of Ph₂PCL dissolved in 2 mL of dichloromethane was slowly added to the mixture at 0° C. The reaction mixture was held at a temperature of 0° C. and stirred for 1 hour. The solution was allowed to warm to room temperature and was stirred for 12 hours. At that time, the solvent was removed under reduced pressure and the residue was extracted with 5 mL of anhydrous THF three times. After removal of the THF solvent, the remaining solid residue was treated with 4 mL of dry CH₃CN three times. The solids were vacuum dried at 40° C. for 6 hours to yield the ditopic ligand, 1,4-triptycene(N(PPh₂)₂)₂, shown in FIG. 1. The yield of the ditopic ligand was 0.27 g (47%). Nuclear magnetic resonance analysis was performed to confirm the structure of the ditopic ligand. ¹H NMR (C₆D₆): δ 7.6-6.28 (m, aromatic H), 5.88 (s, tertiary H) ppm; ³¹P NMR (C₆D₆): δ 60.0 (s) ppm. Anal. Calc. for C₆₈H₅₂N₂P₄: H, 5.13; C, 79.99; N, 2.74%. Found H, 4.6; C, 79.14; N, 3.52%.

Example 2—Ethylene Tetramerization

Multiple ethylene tetramerization runs were performed in a magnetically stirred (1000 rotations per minute (rpm)) stainless steel reactor system (250 ml; commercially available from Buchi), which was equipped with a propeller-like stirrer and injection barrel for charging solvents and reagents. The reactor system was first heated to 110° C., purged several times with argon and ethylene to remove air and moisture, and then cooled to the desired temperature. A solution of the co-catalyst (methylaluminoxane (MAO), modified methylaluminoxane (MMAO), triisobutylaluminium (TiBA), or combinations of these) was then prepared via dilution with a suitable solvent to a total volume of 95 ml. Next, a catalyst solution was prepared when Cr(acac)₃ and the ditopic ligand of Example 1 (1,4-triptycene(N(PPh₂)₂)₂) were separately dissolved in a solvent (1 ml each) before being combined and diluted to a total volume of 5 ml. In examples where the reaction medium was cyclohexane, the solvent of the catalyst solution was either toluene or chlorobenzene. The co-catalyst and catalyst solutions were transferred to the reactor system, which was then pressurized to 45 bar using ethylene to initiate ethylene tetramerization. The temperature of the reactor system was maintained constant during ethylene tetramerization by circulating relatively warm oil through a jacket of the reactor system and relatively cool liquid through a cooling coil of the reactor system as necessary.

After 10 minutes, methanol (1.0 ml) was added to quench ethylene tetramerization. The reactor system was then cooled to approximately 15° C. and slowly depressurized using a needle valve. Next, an aliquot of the liquid inside the reaction system was collected and quantified via gas chromatography (GC) analysis. The liquid remaining in the reaction system was collected, added to acidic methanol (50 ml, 5% HCl ), and stirred at room temperature for 2 hours. Polymer was then filtered from the mixture, washed with distilled water, and stirred in water (200 ml) for 1 hour. This process was repeated four times. Finally, the polymer was filtered and dried in a vacuum oven at 60° C. overnight.

The conditions and results of each run are reported in Table 1.

TABLE 1 Molar Molar 1-hexene 1-octene Polymer Temp. Co- Cr(acac)₃ ratio of ratio of Activity selectivity selectivity selectivity (° C.) Solvent catalyst [μmol] Al/Cr L/Cr [kg · g_(Cr) ⁻¹ · h⁻¹] [wt. %] [wt. %] [wt. %] 45 CyH MMAO-3A 1.0 2000 0.5 1098 24.9 69.2 0.2 45 MeCy MMAO-3A 1.0 2000 0.5 1186 24.6 70.0 0.2 45 DHN MMAO-3A 1.0 2000 0.5 1009 26.0 66.9 1.1 45 TMP MMAO-3A 1.0 2000 0.5 755 28.3 65.7 <0.1 45 PhCl MMAO-3A 1.0 2000 0.5 1717 39.0 56.5 1.5 38 PhCl MMAO-3A 1.0 2000 0.5 1394 34.9 61.1 0.4 30 PhCl MMAO-3A 1.0 2000 0.5 928 20.3 66.3 1.8

The ditopic ligand of Example 1 (1,4-triptycene(N(PPh₂)₂)₂) was compared to a conventional ligand available from Sasol (iPrN(PPh₂)₂) in an ethylene tetramerization process as described hereinabove. It should be noted that the molar ratio of the ditopic ligand of Example 1 to chromium was only 0.5, while the molar ratio of the conventional ligand to chromium was 1. This is because the ditopic ligand incudes two PNP moieties per ligand, while the conventional ligand includes a single PNP moiety per ligand. Accordingly, the ratio of PNP moieties to chromium is the same for both ligands. The results of the ethylene tetramerization process are displayed in Table 2. As displayed in Table 2, the ditopic ligand of Example 1 had a higher activity than the conventional ligand and had a lower polymer selectivity.

TABLE 2 Molar Molar 1-hexene 1-octene Polymer Temp. Co- Cr(acac)₃ ratio of ratio of Activity selectivity selectivity selectivity Ligand (° C.) Solvent catalyst [μmol] Al/Cr L/Cr [kg · g_(Cr) ⁻¹ · h⁻¹] [wt. %] [wt. %] [wt. %] iPrM(PPh₂)₂ 45 PhCl MMAO-3A 1.0 2000 1 1184 18.6 69.9 3.5 Triptycene 45 PhCl MMAO-3A 1.0 2000 0.5 1717 39.0 56.5 1.5 [(NPPh₂₎₂]₂

In a first aspect of the present disclosure, a catalyst system suitable for tetramerizing ethylene to form 1-octene may include a catalyst comprising a chromium compound coordinated with a ligand and a co-catalyst comprising an organoaluminum compound. The ligand may have a chemical structure according to formula (I), wherein at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ have the structure according to formula (II) wherein R_(A), R_(B), R_(C), and R_(D) and the remainder of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.

A second aspect of the present disclosure may include the first aspect, wherein R₃ has a structure according to formula (II) wherein R_(A), R_(B), R_(C), and R_(D) and R₁, R₂, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.

A third aspect of the present disclosure may include the first or second aspects, wherein R₃ has a structure according to formula (II) wherein R_(A), R_(B), R_(C), and R_(D) are independently chosen from a (C₁-C₅₀) hydrocarbyl group, wherein R₁, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) hydrocarbyl group, and wherein R₂, R₄, R₅, R₆, R₈, R₉, R₁₁, and R₁₂ are hydrogen.

A fourth aspect of the present disclosure may include the third aspect, wherein R_(A), R_(B), R_(C), R_(D), R₁, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) linear or branched alkyl group, or a (C₆-C₅₀) aryl group.

A fifth aspect of the present disclosure may include the first aspect, wherein R₁ and R₄ have the chemical structure according to formula (II) wherein R_(A), R_(B), R_(C), and R_(D) and R₂, R₃, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.

A sixth aspect of the present disclosure may include the first or fifth aspects, wherein R₁ and R₄ have the chemical structure according to formula (II) wherein R_(A), R_(B), R_(C), and R_(D) are independently chosen from a (C₁-C₅₀) hydrocarbyl group, wherein R₃, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) hydrocarbyl group, and wherein R₂, R₅, R₆, R₈, R₉, R₁₁, and R₁₂ are hydrogen.

A seventh aspect of the present disclosure may include the sixth aspect, wherein R_(A), R_(B), R_(C), R_(D), R₃, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) linear or branched alkyl group, or a (C₆-C₅₀) aryl group.

An eighth aspect of the present disclosure may include any of the first through seventh aspects, wherein the chromium compound comprises one or more of an organic chromium salt, an inorganic chromium salt, a chromium coordination, and a chromium organometallic complex.

A ninth aspect of the present disclosure may include any of the first through eighth aspects, wherein the chromium compound comprises one or more of chromium trichloride tris-tetrahydrofuran complex, (benzene)tricarbonyl chromium, chromium (III) octanoate, chromium (III) acetylacetonoate, chromium hexacarbonyl, and chromium (III) 2-ethylhexanoate.

A tenth aspect of the present disclosure may include any of the first through ninth aspects, wherein the catalyst comprises the ligand in an amount such that a molar ratio of the ligand to chromium is from 0.1 to 10.0.

An eleventh aspect of the present disclosure may include any of the first through tenth aspects, wherein the organoaluminum compound has a structure according to formula (XIII) wherein R₁₃, R₁₄ and R₁₅ are each selected from the group consisting of a hydrogen atom and an unsubstituted (C₁-C₂₀) linear or branched alkyl group.

A twelfth aspect of the present disclosure may include any of the first through eleventh aspects, wherein the organoaluminum compound comprises one or more of trimethylaluminium, triethylaluminum, tripropylaluminum, tri-iso-butylaluminum, diisoblaylaiuminium hydride, trihexylaluminum, tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, aluminium isopropoxide, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, methylaluminoxane, ethylaluminoxane, and modified methylaluminoxane.

A thirteenth aspect of the present disclosure may include any of the first through twelfth aspects, wherein the catalyst system comprises the co-catalyst in an amount such that a molar ratio of aluminum to chromium is from 0.1 to 10.0.

According to a fourteenth aspect of the present disclosure, a method for tetramerizing ethylene to form 1-octene may include contacting ethylene with the catalyst system of any of the first through thirteenth aspects to form a product comprising 1-octene.

A fifteenth aspect of the present disclosure may include the fourteenth aspect where ethylene is formed in conditions of a reactor pressure from 2 bar to 100 bar and a reactor temperature from 25° C. to 180° C.

The subject matter of the present disclosure has been described in detail and by reference to specific embodiments. It should be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that the component or feature is essential to the particular embodiment or to any other embodiment. Further, it should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.

For the purposes of describing and defining the present disclosure it is noted that the terms “about” or “approximately” are utilized in this disclosure to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “about” and/or “approximately” are also utilized in this disclosure to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”

It should be understood that where a first component is described as “comprising” a second component, it is contemplated that, in some embodiments, the first component “consists” or “consists essentially of” that second component. It should further be understood that where a first component is described as “comprising” a second component, it is contemplated that, in some embodiments, the first component comprises at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or even at least 99% that second component (where % can be weight % or molar %).

Additionally, the term “consisting essentially of” is used in this disclosure to refer to quantitative values that do not materially affect the basic and novel characteristic(s) of the disclosure. For example, a chemical composition “consisting essentially” of a particular chemical constituent or group of chemical constituents should be understood to mean that the composition includes at least about 99.5% of a that particular chemical constituent or group of chemical constituents.

It should be understood that any two quantitative values assigned to a property may constitute a range of that property, and all combinations of ranges formed from all stated quantitative values of a given property are contemplated in this disclosure. It should be appreciated that compositional ranges of a chemical constituent in a composition should be appreciated as containing, in some embodiments, a mixture of isomers of that constituent. In additional embodiments, the chemical compounds may be present in alternative forms such as derivatives, salts, hydroxides, etc. 

What is claimed is:
 1. A catalyst system suitable for tetramerizing ethylene to form 1-octene, the catalyst system comprising: a catalyst comprising a chromium compound coordinated with a ligand; and a co-catalyst comprising an organoaluminum compound, wherein: the ligand has the chemical structure:

wherein at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ have the structure:

wherein R_(A), R_(B), R_(C), and R_(D) and the remainder of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.
 2. The catalyst system of claim 1, wherein R₃ has the structure:

wherein R_(A), R_(B), R_(C), and R_(D) and R₁, R₂, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.
 3. The catalyst system of claim 1, wherein R₃ has the chemical structure:

wherein R_(A), R_(B), R_(C), and R_(D) are independently chosen from a (C₁-C₅₀) hydrocarbyl group; wherein R₁, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) hydrocarbyl group; and wherein R₂, R₄, R₅, R₆, R₈, R₉, R₁₁, and R₁₂ are hydrogen.
 4. The catalyst system of claim 3, wherein R_(A), R_(B), R_(C), R_(D), R₁, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) linear or branched alkyl group, or a (C₆-C₅₀) aryl group.
 5. The catalyst system of claim 1, wherein R₁ and R₄ have the chemical structure:

wherein R_(A), R_(B), R_(C), and R_(D) and R₂, R₃, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, and R₁₂ are independently chosen from a hydrogen or a (C₁-C₅₀) hydrocarbyl group.
 6. The catalyst system of claim 1, wherein R₁ and R₄ have the chemical structure:

wherein R_(A), R_(B), R_(C), and R_(D) are independently chosen from a (C₁-C₅₀) hydrocarbyl group; wherein R₃, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) hydrocarbyl group; and wherein R₂, R₅, R₆, R₈, R₉, R₁₁, and R₁₂ are hydrogen.
 7. The catalyst system of claim 6, wherein R_(A), R_(B), R_(C), R_(D), R₃, R₇, and R₁₀ are independently chosen from a (C₁-C₅₀) linear or branched alkyl group, or a (C₆-C₅₀) aryl group.
 8. The catalyst system of claim 1, wherein the chromium compound comprises one or more of an organic chromium salt, an inorganic chromium salt, a chromium coordination, and a chromium organometallic complex.
 9. The catalyst system of claim 1, wherein the chromium compound comprises one or more of chromium trichloride tris-tetrahydrofuran complex, (benzene)tricarbonyl chromium, chromium (III) octanoate, chromium (III) acetylacetonoate, chromium hexacarbonyl, and chromium (III) 2-ethylhexanoate.
 10. The catalyst system of claim 1, wherein the catalyst comprises the ligand in an amount such that a molar ratio of the ligand to chromium is from 0.1 to 10.0.
 11. The catalyst system of claim 1, wherein the organoaluminum compound has the structure:

wherein R₁₃, R₁₄, and R₁₅ are each selected from the group consisting of a hydrogen atom and an unsubstituted (C₁-C₂₀) linear or branched alkyl group.
 12. The catalyst system of claim 1, wherein the organoaluminum compound comprises one or more of trimethylaluminium, triethylaluminum, tripropylaluminum, tri-iso-butylaluminum, diisobutylahiminiurn hydride, trihexylaluminum, tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, aluminium isopropoxide, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, methylaluminoxane, ethylaluminoxane, and modified methylaluminoxane.
 13. The catalyst system of claim 1, wherein the catalyst system comprises the co-catalyst in an amount such that a molar ratio of aluminum to chromium is from 0.1 to 10.0.
 14. A method for tetramerizing ethylene to form 1-octene, the method comprising contacting ethylene with the catalyst system of claim 1 to form a product comprising 1-octene.
 15. The method of claim 14, wherein the ethylene is formed in conditions of: a reactor pressure from 2 bar to 100 bar; and a reactor temperature from 25° C. to 180° C. 